Please help me. I have a strange rattle, I can't find it.
 

Its coming from the back, and it sounds like its around the backseat headrest area, or possibly in the trunk. Its not a constant rattle. It doesn't even happen when going over a bump.

Its sounds like a loose piece of plastic or wiring hitting the metal frame of the car somewhere. Like a swinging sound. I'm going crazy.

I have the same thing in my BRZ, not sure what it is though

Could it be that the back seats are not securely fastened? check if the two buttons are pressed down. My car came from dealership with one side unsecured and flopping around.

Doesn't seem like it. They are securely in place. I popped the trunk lining on the sides, and taped the wiring to the car to see if that's what it was. I doubt it though well see when i take her out for lunch. If anyone has the same problem, and figures it out please share.

Could it be speaker?

Does the sound change with the rear seats up vs down?
You might want to check below thread out.
Especially post #38 on page 2.
http://www.ft86club.com/forums/showt...?t=7181&page=2

Do you have tint? Could be broken tabs in the 3rd brake light.

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i have no tint and leave my seats folded down. sounds more like its coming from the spare tire area for me

How do I check this?
I do have tint.

Check that the emergency trunk release handle (glow in the dark handle) is fully seated into its holder.

Jiggle the 3rd brake light by hand and see if its loose.

I did a couple days ago, thought I found the culprit, but it turned to not be that. :( I taped it up, and still get the damn noise.

My rattle was speaker tabs
 

I bent the tabs that go thru the deck to hold the speakers in place. They weren't bent at all, so I gave 'em a bit of a bend and my rattling is gone. It was TOTALLY annoying.

I'm having the same problem and it drove me crazy. I had my girlfriend lie in the back with the back seats folded over so she can tell me where the sound is coming from. She said it came from "in between the trunk and the back seats from the top section" so I'd say somewhere around the 3rd brake light.

If anyone figures this out, do let us know!